1. Field of the Invention
The present invention relates generally to the field of multifiber connectors and, more specifically, to molded fiber optic ferrules with an integral reference surface for end face geometry measurement.
2. Description of the Related Art
Optical fibers are used for a variety of applications including voice communications, data transmission and the like. In order to interconnect a plurality of optical fibers with a minimum amount of attenuation, a pair of multifiber connectors is preferably mated such that the opposing optical fibers are biased into contact with one another. To achieve optimal transmission without utilizing refractive index matching gel, the multifiber connectors must be precisely aligned in order to correspondingly align the individual optical fibers in the connectors. This alignment is typically provided by guide pins that extend outwardly from the end face of a male multifiber ferrule for insertion into corresponding guide pin openings, grooves or other structures defined by a female multifiber ferrule. In addition to precise alignment, the geometry of the ferrule and, in particular, the polish geometry of the end face of the ferrule, is extremely important to insure proper fiber-to-fiber contact. In this regard, at least the portion of the end face of each ferrule that is proximate to the optical fibers is preferably polished to define a plane extending perpendicular to the longitudinal axis defined by the guide pin openings and, therefore, perpendicular to the fiber bores. In addition, the planar surface defined by the portion of the end face of each ferrule proximate to the fiber bores is precisely positioned relative to the ends of the optical fibers. For example, with proper polish geometry, the optical fibers will extend by a predetermined distance beyond the end face of the ferrule so that fiber-to-fiber contact between opposing optical fibers is established. If, however, the polish geometry is not precisely defined, fiber-to-fiber contact may be prevented or otherwise obstructed by contact between those portions of the end faces of the opposing ferrules that extend beyond the ends of the optical fibers.
In order to monitor the polish geometry and the resulting quality of each ferrule, it is desirable to determine the planarity of the end face of the ferrule and the angle of the end face relative to the guide pin openings. As such, referring to prior art FIGS. 1a-b, a conventional ferrule 30 is shown in which an end face reference surface 32, also referred to herein as the “region of interest,” is measured for planarity. The end face reference surface 32 is an area on the end face 34 of the ferrule 30 in the vicinity of the plurality of fiber bores 42. Truncated measurement pins 33 having very precisely machined ends that extend from the end face 34 of the ferrule 30 are used to determine if the end face reference surface 32 of the ferrule 30 has been properly molded or machined to be planar. In order to determine the planarity of end face reference surface 32, the measurement pins 33 are inserted into guide pin openings 36 to define a measurement pin reference surface 38. Referring to FIG. 1b, the measurement pins 33 are machined to be very flat on one of their ends. The plane defined by the measurement pin reference surface 38 of one or both of the measurement pins 33 is then compared to the end face reference surface 32 using an interference vision system, such as an interferometer having 3D capabilities. After comparative measurements have been made and the planarity of the end face reference surface 32 confirmed, the measurement pins 33 are removed from the guide pin openings 36 and replaced with conventional guide pins to produce a male ferrule. A female ferrule is produced with vacant guide pin openings 36 operable for receiving the guide pins of a respective male ferrule. Predetermined lengths of optical cable may then be produced by combining sections of cable comprising mating male and female ferrules. An example of a multi-fiber ferrule measured using truncated pins can be found in U.S. Pat. No. 5,867,621 issued to Luther et al.
There are several disadvantages associated with using truncated precision measurement pins 33 to measure the planarity of the end face reference feature 32 and/or the angularity of the end face 34. For one, the measurement pins 33 are very expensive to manufacture because of the very precise machining of one of their ends. Furthermore, the measurement pins 33 may be easily lost due to their extremely small size. Also, when using the ends of the measurement pins 33 as a reference surface, it is necessary to make the optical measurements using a relatively expensive interference vision system having 3D capabilities. Still further, with conventional multifiber ferrules, male multifiber ferrules cannot be measured for planarity after assembly due to the difficulty in removing the guide pins without damaging the ferrule assembly.
In particular instances, it is desired to produce a ferrule having an end face with an angle other than normal (i.e., perpendicular) to the longitudinal axis of the ferrule body. In such cases, the angle is typically introduced by machining the end face of the ferrule subsequent to the molding process. By machining the angle as opposed to molding it, the end face of every ferrule must be individually machined after the ferrule is removed from the mold. This subsequent machining step leads to a decrease in ferrule uniformity and an increase in ferrule production time. Therefore, it would be desirable to rapidly and economically produce a large number of substantially identical ferrules having an end face with a predetermined angle relative to the longitudinal axis of the ferrule body, without having to machine each ferrule subsequent to the molding process.
Thus, there is a need in the art for a fiber optic ferrule that eliminates the need for using truncated precision measurement pins and an interference vision system having 3D capabilities to determine the planarity of the region of interest on the end face of the ferrule. Such ferrule should have integral geometry features that permit planarity measurements of at least the region of interest of the end face, and angularity measurements of the entire end face, to be determined more readily and more economically. Such ferrule should substantially reduce ferrule manufacturing, assembly and quality inspection times. Such ferrule should allow for region of interest planarity and end face angularity measurements to be made for both male and female ferrules after ferrule assembly and throughout the life of the ferrule. Such ferrule should eliminate the step of having to machine a predetermined angle on the end face of the ferrule subsequent to the molding process.